#include <cstdlib>
#include <iostream>
#include "asio.hpp"

using asio::ip::udp;

class server
{
public:
    server(asio::io_context& io_context, short port)
        : socket_(io_context, udp::endpoint(udp::v4(), port))
    {
        do_receive();
    }

    void do_receive()
    {
        socket_.async_receive_from(
            asio::buffer(data_, max_length), sender_endpoint_,
            [this](std::error_code ec, std::size_t bytes_recvd)
        {
            if(!ec && bytes_recvd > 0)
            {
                do_send(bytes_recvd);
            }
            else
            {
                do_receive();
            }
        });
    }

    void do_send(std::size_t length)
    {
        socket_.async_send_to(
            asio::buffer(data_, length), sender_endpoint_,
            [this](std::error_code /*ec*/, std::size_t /*bytes_sent*/)
        {
            do_receive();
        });
    }

private:
    udp::socket socket_;
    udp::endpoint sender_endpoint_;
    enum { max_length = 1024 };
    char data_[max_length];
};

int main(int argc, char* argv[])
{
    try
    {
        if(argc != 2)
        {
            std::cerr << "Usage: async_udp_echo_server <port>\n";
            return 1;
        }

        asio::io_context io_context;

        server s(io_context, std::atoi(argv[1]));

        io_context.run();
    }
    catch(std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}